1. Field of the Invention
The invention is directed to an improved fuel injection valve for internal combustion engines.
2. Description of the Prior Art
A fuel injection valve of the type with which this invention is concerned is disclosed by the reference DE 198 57 244 A1 in which a valve body has a bore in which a piston-shaped valve member is contained so that it can slide longitudinally counter to a closing force. At its end oriented toward the combustion chamber, the valve member transitions into a valve sealing surface, which cooperates with a valve seat and thus controls the opening of at least one injection opening. The valve member is guided in the bore in a sealing section oriented away from the combustion chamber and in a guiding section oriented toward the combustion chamber. The guiding section includes an annular collar remote from the combustion chamber, which is separated by an annular groove from lateral recesses embodied on the valve member so that fuel can flow past through these recesses, between the wall of the bore and the valve member. On its side oriented toward the combustion chamber, the annular collar has a control edge, which cooperates with a sealing edge embodied on the wall of the bore. In addition, a bore is embodied in the valve member, which extends obliquely in relation to the longitudinal axis of the valve member and connects the pressure chamber, which is embodied on the side of the annular collar oriented away from the combustion chamber, between the valve member and the wall of the bore, to one of the recesses in the guiding section of the valve member. The bore is embodied as a throttle bore so that fuel can flow in a throttled fashion from the pressure chamber to the recesses and therefore to a second pressure chamber, which is embodied between the valve member and the wall of the bore, between the guiding section and the valve sealing surface. When the fuel injection valve is closed, the valve sealing surface of the valve member rests against the valve seat and the control edge on the annular collar is disposed closer to the combustion chamber than the sealing edge so that the first pressure chamber is connected to the second pressure chamber only by means of the throttle bore. If an injection is to take place, highly pressurized fuel is introduced into the first pressure chamber and flows from there through the throttle bore into the second pressure chamber as well. If the hydraulic force on the valve member is sufficient to move it away from the valve seat counter to the closing force, then the valve sealing surface lifts up from the valve seat and fuel is injected through the injection opening into the combustion chamber of the engine. As long as the annular collar is disposed closer to the combustion chamber than the sealing edge, only a small amount of fuel can travel from the first pressure chamber, through the throttle bore, and into the second pressure chamber. In the course of the opening movement of the valve member, when the control edge passes the sealing edge, then the first pressure chamber is connected to the second pressure chamber by means of the annular groove and the recesses in the guiding section of the valve member and fuel can flow from the first pressure chamber into the second pressure chamber in a virtually unthrottled manner. This increases the pressure in the second pressure chamber and consequently the rate of injection so that on the whole, a shaping of the rate-of-discharge curve is achieved in which only a small amount of fuel is injected at the beginning of the opening stroke motion due to the relatively low pressure in the second pressure chamber, and the main quantity of the fuel is injected at high pressure only in the subsequent main injection. In this connection, however, the known fuel injection valve has the disadvantage that the necessary throttle bore is expensive to produce, which makes the manufacture quite cost intensive. There is also the disadvantage that because of the necessary clampings of the valve member, the throttle bore must already be produced in an early stage of the manufacturing process, which makes it impossible to subsequently adapt the throttle bore to other tolerances that come up.